1. Field of the Invention
The present invention relates to a small size electronic part such as, for example, an angular velocity sensor, acceleration sensor, mechanical filter, etc. to a small size electronic part having an electrode terminal output providing an electric signal and a method for manufacturing such and a method for forming a via hole for use in such a small size electronic part.
2. Description of the Related Art
Generally, an angular velocity sensor, acceleration sensor, mechanical filter, etc. is widely known as a small size electronic part produced by a silicon micromachining technique. Further, such a small size electronic part comprises, for example, a silicon substrate, and glass substrates which are bonded to the upper and lower surfaces of the silicon substrate, respectively. A functional element for detecting an angular velocity is formed in the silicon substrate, for example, and the functional element is sealed by the two glass substrates.
Such a conventional small size electronic part may be mounted on the surface of a circuit board. Further, in order to make the circuit board small-sized, it is required to reduce the mounting surface of the small size electronic part. To this end, there has been known a small size electronic part in which a via hole passing through the upper glass substrate is formed and an electric signal is lead out from the functional element through the via hole so that the functional element and circuit board are electrically connected (See Japanese Unexamined Patent Publication No. 10-213441).
More specifically, in the small size electronic part, a glass substrate having a via or through hole therein is bonded to a silicon substrate, and conductive paste (or metal) is filled in the through hole, so that an external circuit board is made to be electrically connected to the functional element using the conductive paste.
The aforementioned conventional technique has a drawback that, when the conductive paste is filled in the through hole, air bubbles may be produced in the conductive paste. This causes a problem of contact failure caused by these air bubbles and the reliability is therefore decreased.
In particular, when the communicating hole is made of a small diameter and given that the electronic parts are made small-sized, air bubbles are more likely to be produced, and therefore in order to avoid this the through hole must be made of a larger diameter and accordingly there has been a problem that the part size is increased and the mounting surface increases in size.
Moreover, because the thermal expansion coefficient of the conductive paste is different from that of glass material, when a temperature change is produced in a small size electronic part, there are cases in which cracks occur in the glass substrate.
In order to lead out an electric signal from a functional element reliably, it is possible to provide a conductive film on the internal wall surface of the communicating hole as a substitute for the conductive paste. In this case, however, when a through hole is processed in a glass substrate by sandblasting, chips (broken pieces of glass or their traces) may be produced on the side of the surface of the glass substrate to which a silicon substrate is joined. Because of this, when the surfaces of a silicon substrate and glass substrate are joined, a step-like portion is produced between the silicon substrate and the through hole by the chip. As a result, when a conductive film is processed on the internal wall surface of the through hole, the conductive film may be disconnected by these step-like portions and there is a problem of decreased yields.